The present invention relates to visual displays, and more particularly to addressable, reusable, paper-like visual displays, and to gyricon or twisting-ball displays.
Since ancient times, paper has been a preferred medium for the presentation and display of text and images. The advantages of paper as a display medium are evident. For example, it is lightweight, thin, portable, flexible, foldable, high-contrast, low-cost, relatively permanent, and readily configured into a myriad of shapes. It can maintain its displayed image without using any electricity. Paper can be read in ambient light and can be written or marked upon with a pen, pencil, paintbrush, or any number of other implements, including a computer printer.
Unfortunately, paper is not well suited for real-time display purposes. Real-time imagery from computer, video, or other sources cannot be displayed directly with paper, but must be displayed by other means, such as by a cathode-ray tube (CRT) display or a liquid-crystal display (LCD). Typically, real-time display media lack many of the desirable qualities of paper, such as physical flexibility and stable retention of the displayed image in the absence of an electric power source.
Attempts have been made to combine the desirable qualities of paper with those of real-time display media in order to create something that offers the best of both worlds. That something can be called electric paper.
Like ordinary paper, electric paper preferably can be written and erased, can be read in ambient light, and can retain imposed information in the absence of an electric field or other external retaining force. Also like ordinary paper, electric paper preferably can be made in the form of a lightweight, flexible, durable sheet that can be folded or rolled into tubular form about any axis and conveniently placed into a shirt or coat pocket, and then later retrieved, re-straightened, and read substantially without loss of information. Yet unlike ordinary paper, electric paper preferably can be used to display full-motion and other real-time imagery as well as still images and text. Thus it is adaptable for use in a computer system display screen or a television.
The gyricon display, also called the twisting-ball display, rotary ball display, particle display, dipolar particle light valve, etc., offers a technology for making a form of electric paper. Briefly, a gyricon display is an addressable display made up of a multiplicity of optically anisotropic balls, each of which can be selectively rotated to present a desired face to an observer. For example, a gyricon display can incorporate balls each having two distinct hemispheres, one black and the other white, with each hemisphere having a distinct electrical characteristic (e.g., zeta potential with respect to a dielectric fluid) so that the balls are electrically as well as optically anisotropic. The black-and-white balls are embedded in a sheet of optically transparent material, such as an elastomer layer, that contains a multiplicity of spheroidal cavities and is permeated by a transparent dielectric fluid, such as a plasticizer. The fluid-filled cavities accommodate the balls, one ball per cavity, so as to prevent the balls from migrating within the sheet. A ball can be selectively rotated within its respective fluid-filled cavity, for example by application of an electric field, so as to present either the black or the white hemisphere to an observer viewing the surface of the sheet. Thus, by application of an electric field addressable in two dimensions (as by a matrix addressing scheme), the black and white sides of the balls can be caused to appear as the image elements (e.g., pixels or subpixels) of a displayed image.
An exemplary gyricon display 10 is shown in side view in FIG. 1 (PRIOR ART). Bichromal balls 11 are disposed in an elastomer substrate 12 that is swelled by a dielectric fluid creating cavities 13 in which the balls 11 are free to rotate. The balls 11 are electrically dipolar in the presence of the fluid and so are subject to rotation upon application of an electric field, as by matrix-addressable electrodes 14a, 14b. The electrode 14a closet to viewing surface 15 is preferably transparent. An observer at I sees an image formed by the black and white pattern of the balls 11 as rotated to expose their black or white faces (hemispheres) to the viewing surface 15 of substrate 12.
Gyricon display technology is described further in the patents incorporated by reference hereinabove. In particular, U.S. Pat. No. 5,389,945 (Sheridon, "Writing System Including Paper-Like Digitally Addressed Media and Addressing Device Therefor") shows that gyricon displays can be made that have many of the desirable qualities of paper, such as flexibility and stable retention of a displayed image in the absence of power, not found in CRTs, LCDs, or other conventional display media. Gyricon displays can also be made that are not paper-like, for example, in the form of rigid display screens for flat-panel displays.
Typically, known gyricon displays are made up of bichromal balls that are black in one hemisphere and white in the other. Other kinds of balls are also known. For example, U.S. Pat. No. 4,261,653 (Goodrich) shows a multilayer ball, although it is made at least in part from glass and its use depends on an addressing scheme involving high-frequency electric fields.
Although the gyricon display represents an important step toward the goal of electric paper, there is still a long way to go. For example, a gyricon display constructed of black-and-white balls cannot provide a multicolor image. As another example, a gyricon display designed to operate in ambient reflected light cannot provide a projective or transmissive display. What is needed is an advanced gyricon display technology that can provide a more full range of display capabilities and, in particular, can provide color projective and transmissive imaging.